Proposed workshop build
- Thread starter DomP
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Jameshow
Established Member
I'd put epoxy paint very osb or ply. Primer first then top be coat, then you can see when your wearing through.
DomP
Established Member
I'm also sure I read MikeG say that piers were really only suitable for workshops up to a certain size which fell well below my 7 x 5m
Inspector
Nyuck, Nyuck, Nyuck!
Given that very large structures have been/are built on piers a worksop of any size you are likely to build will not be restricted by that type of foundation. Pier Foundations | House Plans and More Don't forget that many river and ocean side docks are built on them and they can be huge. If you prefer a slab then that is a preference more than anything else.
Pete
Pete
Jameshow
Established Member
Surely it depends on the loads the piers have to maintain. And the strength if the floor?
A shipping container can be lifted by its corners with 20t weight inside.
I've put an 6x5m office unit together with pillars at 2m intervals and it's been fine.
It depends on the loading your anticipating on putting through the floor?
If a Watkins or similar then beefed up flooring or better still concrete floors are the way to go?
If hobby tools then 22mm osb on 16cm c-c will be fine?
heimlaga
Established Member
Up here where we have the ground freezing down to two metres depth pier foundations generally work best for uninsulated wooden buildings which are rather elastic. Because the piers always rise and sink a bit.
I would not recommend a pier foundation for a workshop of that size. Because there are too many unknown variables with large movable weights inside.
What is the type of subsoil?
A raft type foundation made from concrete is generally made thicker around the edges and thinner in the middle. 40 cm thick around the edges and 12 cm for the rest is a fairly common thickness. If the rebar is 5 cm from the surface in K25 or even better K30 concrete it is well protected against rust.
If the sub soil is solid enough it is usually easier to dig a foundation trench around the perimeter and fill some gravel or macadam or sand in the bottom of it and pour a 50-60 cm wide and 20 cm thick footing all around the perimeter in simple wooden shutterings. 3-4 10 mm rebars along the lengt and 8 mm bars across at 50 cm centers is often enough reinforcement. On top of that a concrete block wall that reaches at least 40 cm above ground. A strip of roofing felt atop the uppermost block course and the wooden sill on top of that.
Then you can either lay floor joists on top of the block walls and build a wooden floor or pour a concrete floor inside depending on what materials are affordable to you.
For a building of this size the framing should normally be 2x4 cc 60 cm around here but in subtropical Hertfordshire with very small snow loads it might possible be enough even with 2x3. If you can get unplaned real 2x5 which is 50x100 you get significantly more load bearing capacity for the same cost as the weaker undersize planed 2x4.
I have a Batchelor's degree in structural engineering though I ended up unemployed and now work as a restoration carpenter and joiner.
I would not recommend a pier foundation for a workshop of that size. Because there are too many unknown variables with large movable weights inside.
What is the type of subsoil?
A raft type foundation made from concrete is generally made thicker around the edges and thinner in the middle. 40 cm thick around the edges and 12 cm for the rest is a fairly common thickness. If the rebar is 5 cm from the surface in K25 or even better K30 concrete it is well protected against rust.
If the sub soil is solid enough it is usually easier to dig a foundation trench around the perimeter and fill some gravel or macadam or sand in the bottom of it and pour a 50-60 cm wide and 20 cm thick footing all around the perimeter in simple wooden shutterings. 3-4 10 mm rebars along the lengt and 8 mm bars across at 50 cm centers is often enough reinforcement. On top of that a concrete block wall that reaches at least 40 cm above ground. A strip of roofing felt atop the uppermost block course and the wooden sill on top of that.
Then you can either lay floor joists on top of the block walls and build a wooden floor or pour a concrete floor inside depending on what materials are affordable to you.
For a building of this size the framing should normally be 2x4 cc 60 cm around here but in subtropical Hertfordshire with very small snow loads it might possible be enough even with 2x3. If you can get unplaned real 2x5 which is 50x100 you get significantly more load bearing capacity for the same cost as the weaker undersize planed 2x4.
I have a Batchelor's degree in structural engineering though I ended up unemployed and now work as a restoration carpenter and joiner.
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Inspector
Nyuck, Nyuck, Nyuck!
Some areas of Canada do a variation of the footings and block walls you mention heimlaga by pouring a solid concrete wall on top of the footings. When I was a pup out of high school near Vancouver BC I worked as a framers helper. We put in the footings and forms for modest sized houses without basements, for the concrete, poured in one go. Footings were of 2x6 or 2x8 held with stakes a couple feet apart and 1x2 were nailed across the tops. Rented plywood forms were set on top of the 1x2s. The outside sheets against a 2x4 also nailed to the 1x2s for locating. When ready the concrete trucks and sometimes a pumper truck showed up and the concrete poured into the forms which then flowed down into the footings. These were for foundation walls from 2 to 4 feet high. Once the tops of the foundation walls were troweled smooth and level we went home for the weekend. The following week the forms were striped, scraped clean and rental company picked them up. The 2x material for the footings were cleaned up and reused in the house. The only thing left of the forms were the broken bits of 1x2 across the top of the footing and through the walls. No termites so that wasn't a concern. Then the wood floor was built or the walls were built with the slab being poured after the plumbers had placed all their pipes. I like the method much more that the bricks on a slab method used by many on the forum as there is never any chance of water getting through any of the mortar holding the bricks.
This area also has frost like you do but the practice for piers is to use helical/screw piles going down at least 10' or until enough resistance is met. Plastic sleeves on the outside of the screw pile lets the ground heave by sliding along with the frozen dirt. Quick to install and no digging needed.
Sorry for the diversion. Back to the regularly scheduled progam.
Pete
This area also has frost like you do but the practice for piers is to use helical/screw piles going down at least 10' or until enough resistance is met. Plastic sleeves on the outside of the screw pile lets the ground heave by sliding along with the frozen dirt. Quick to install and no digging needed.
Sorry for the diversion. Back to the regularly scheduled progam.
Pete
DomP
Established Member
This is why I've not settled on a method yet, one person says piers will be fine the next that they are totally unsuitable
Jameshow
Established Member
What's your intended usage and weigh needs??
Dibs-h
Established Member
Time to talk to or go see a Structural Engineer. A 7x5 (or so) metre structure isn't small.
I built one - 7.5m x 5m, dual pitched - It's been years, but somewhere around 12-14 cubic metres of concrete (C35) went in along with the more steel than I wish to remember. Admittedly mine had a cantilever element - but even without it, I wouldn't have done it based on a "back of a fag packet" sketch.
The thread on my build is on here somewhere - feel free to check it out and see the foundations for yourself.
Jameshow
Established Member
I'd go with your gut feeling.
150mm all over.
I used 300/150mm raft on a double story extension in. 2008.
Your loads in the middle will be higher but your edge loads will be lighter hence why 150mm all over.
As you have tree roots I'd go 150mm over 100mm.
DomP
Established Member
A raft is really the only way to go I believe, I can't lose height and having a large step up in makes getting machinery and motorbikes in a farce. I'm thinking 125mm thickened at the edges with A142 mesh laid on an mot base with blinding and membrane. 3 courses of brick or block then build my frame from there.
Jameshow
Established Member
I used to have a Triumph 500 Daytona twin, great bike apart from the oil leaks from the pushrod tubes.
With a raft I would just use 6 inches and mesh so as you can fill it up with any machinery that takes your fancy and not worry about the ground below, it is a do it once job that cannot be altered later so no point in cutting corners.
DomP
Established Member
Yes, following MikeG's advice he suggests that mesh must be 50mm from either top or bottom of the raft and NOT centre as it has no benefit, I presume it as its neither under stretch or compression but in a neutral position. This dictates that a raft has to be over 100mm thick.
DomP
Established Member
I love my 675 but don't ride it enough, I also have an xs650b that I'm lightly restoring, it smells so good.
Beech trees are wont to drop limbs quite randomly so make sure you're not under it.
DomP
Established Member
I'm getting close to the point of starting this now but still don't see how the dp membrane has continuity after the raft shuttering is removed, there will be a gap between it and where my 3 courses of engineering bricks end. Am I at risk of driving rain finding a way between the raft and brick course? Maybe I need to post a sketch to fully explain my dilemma.
It does not give continuity if you follow Mike's design, moisture can still enter the slab from the edges and get into/through your brick course. Per Mike's diagram you then have a DPC on top of your brick course to prevent moisture entering the timber structure and you have another barrier between slab and flooring (500 gauge polythene to keep any moisture in the slab away from your floor.
If you use the concrete slab as your finished floor and you want it isolated from any moisture source you need another design. If you google 'concrete slab floor wall detail' you get lots of different design, for example this one, where you can see extra elements to give continuity of the DPM around the slab.
Fitz
